1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium.
2. Related Art
Magnetic recording devices such as hard disk drives (HDDs) have come into popular and widespread use as a result of spread of personal computers. In recent years, the advent of the Internet and DVDs providing high-resolution image information has rapidly increased the amount of information to be processed by magnetic recording devices, and therefore there has been a growing demand for larger-capacity magnetic recording devices. Further, miniaturization of HDDs to be installed in mobile devices such as mobile phones, car navigation systems, and MP3 players is progressing, and therefore demand for higher-density HDDs is also growing. It can be said that such a situation has been produced by a significant increase in recording density of HDDs. The recording density of HDDs can be increased by forming smaller magnetic recording marks. Formation of smaller magnetic recording marks requires a smaller write head, a reproducing head capable of detecting a smaller magnetic field, and a magnetic recording medium on which smaller magnetic recording marks can be written stably.
Conventionally, formation of smaller magnetic recording marks on a magnetic recording medium has been achieved by reducing the particle size of magnetic particles constituting a magnetic recording layer formed by sputtering. However, the use of smaller magnetic particles makes it more difficult to solve a problem of so-called thermal fluctuation caused by deterioration of thermal stability of micro magnetic particles. A problem of thermal fluctuation can be solved by using a magnetic material having a high coercive force to improve the thermal stability of the magnetic material itself. This, however, requires a stronger write magnetic field in spite of the fact that a write magnetic field generated by a write head is approaching its limit.
In view of the above fact, there has been proposed a patterned medium having a structure significantly different from that of a conventional magnetic recording medium (see, for example, JP-A 2004-295989 (KOKAI)). Such a patterned medium has recording cells as minimum recording units. The recording cells are previously formed by lithography so as to be arranged in recording tracks. In the case of a conventional magnetic recording medium, even when a minimum recording mark is written on a magnetic recording layer formed by sputtering, the mark is written on a cluster of a few dozen to a few hundred magnetic particles. On the other hand, in the case of a patterned medium, the size of each magnetic particle can be increased to the size of a recording cell formed by lithography, which makes it possible to ultimately solve a problem of thermal fluctuation resulting from the particle size reduction of magnetic particles.
Meanwhile, manufacturing of patterned media requires an etching mask for etching a magnetic film. Usually, such an etching mask is formed by exposing a coated film formed by coating a solution of a polymeric material to an energy beam such as a light or electron beam to form a pattern. In the case of a so-called imprint method, a pattern is formed by pressing a concavo-convex pattern against a coated film of a polymeric material formed in the same manner as described above.
On the other hand, in the case of manufacturing of media for HDDs, a vacuum environment is maintained until the formation of a protection layer is completed, which allows very high-throughput and low-cost media production.
As described above, since the manufacturing of patterned media uses a coated film, it is necessary to take a disk out of a vacuum environment in the course of production. This reduces throughput, thereby making it difficult to achieve low-cost disk production.
Further, it is very difficult to form a coated film having a uniform thickness over the entire surface of a disk. Particularly, the thickness of the coated film varies widely in a disk edge portion so that it is impossible to carry out uniform etching in the disk edge portion.
Furthermore, when a coated film is formed on one surface of a disk, it is inevitable that in the disk edge portion, the material of the coated film reaches the other surface onto which the material is not applied. Therefore, it is very difficult to form a pattern on the entire surface of each of both sides of the disk, which makes it impossible to achieve high-density recording.
The etching mask must be completely removed before a recording medium is completed. If the etching mask remains in the recording medium, a head cannot come sufficiently close to the medium. This makes it difficult to carry out writing and reading of micro recording marks, that is, it becomes difficult to achieve the intended purpose of patterned media. Usually, a resist material used in producing electronic devices is removed by wet treatment using an appropriate solvent or releasing agent or by oxygen plasma treatment. In a case where wet treatment is carried out using a solvent or a releasing agent, it is necessary to take a disk out of a vacuum environment in the course of production. This reduces throughput, thereby making it impossible to achieve a low-cost disk production process. On the other hand, in a case where oxygen plasma treatment is carried out, there is a possibility that a magnetic film is damaged so that an SN ratio is degraded.
As has been described above, according to a conventional method for manufacturing a patterned medium, it is difficult to produce a medium capable of high-density recording at low cost.